IT’S been six years since The X-Files last aired on TV and 10 years since Mulder and Scully hit the big screen for 1998’s Fight The Future. So, the big question surrounding I Want To Believe was always going to be whether the paranormal duo had waited too long to return to our screens?

But while the US box office suggests the answer to that question is yes, true fans of the series will find that their own faith is rewarded with a deeply involving new entry into the saga.

If anything, The X-Files: I Want To Believe has suffered from bad timing. Arriving in the shadow of The Dark Knight, it was always going to struggle to attract the size of audience needed to confirm it as a blockbuster hit. But it’s not a blockbuster.

Whereas Fight The Future aspired to Independence Day-style spectacle, I Want To Believe is a much more intimate tale – a serial killer episode with psychic associations that also serves as a deeply involving personal story.

Like The Dark Knight and Wall-E before it, the film is also a deeply intelligent and thought-provoking exploration of science and faith that exists – and benefits from – it’s moral complexity.

It does have faults and sometimes struggles to escape the notion that it would have worked better on the small screen, but for long-time devotees of the series there’s plenty to savour.

The plot, which has hitherto remained as closely guarded a secret as Roswell itself, finds Mulder (David Duchovny) and Scully (Gillian Anderson) being asked by the FBI to come back and help them with a case involving the disappearance of one of their agents.

If they agree, their past will be forgiven, but they must also work with a mysterious psychic, Father Joe (Billy Connolly), an ex-paedophile, whose visions seem to hold the key to the mystery. Needless to say, Scully is sceptical but Mulder wants to believe and the subsequent investigation challenges both agents to confront their faith and their relationship with each other.

Although devised as a stand-alone case (in the traditions of some of the best episodes in the show’s history), the emphasis is evenly divided between the crimes and the personal baggage of the people involved.

And the film’s at its most riveting when confronting the big issues – for Scully, the decision of whether to proceed with a painful experimental surgery that could save a young boy’s life and to stick by Mulder as he re-engages with his dark side; for Mulder, exorcising the demons of his past (his missing sister) and clearing his reputation; and for Father Joe, whether his involvement in the case is a shot at redemption or something more sinister.

All three actors excel. Connolly, in particular, deserves praise for underplaying his character and emerging as a genuinely troubled soul who may or may not be worthy of forgiveness, while Anderson and Duchovny pick up their chemistry almost effortlessly and the direction their relationship takes gives rise to a genuinely poignant conclusion.

Less successful are the inclusion of two new FBI agents, in the form of Xzibit’s Mosley Drummy and Amanda Peet’s Dakota Whitney, who feel under-developed, or the central case itself, which feels a little muddled. There is a creepiness about the story (involving severed body parts and black market trading of organs) but it lacks any real big scares and almost peters out.

But for true X-Files fans, it’s the ability to catch up with Mulder and Scully and find out what has happened to them in the past six years that should prove the biggest attraction, and co-writer and director Chris Carter [with the help of series regular Frank Spotnitz] does not disappoint.

His film, while deliberately low-key and understated, is a satisfying experience that even has the audacity to leave some of the questions it poses unanswered – in keeping with the long-held traditions of the show.

Fans must now hope that the “disappointing” US opening figures don’t spell the end for possible future adventures, particularly as Carter and company have expressed an interest in seeing the alien conspiracy arc through to its conclusion in 2012. There’s still plenty of life in The X-Files yet.